Borrowing Power And Serviceability Explained

01What "borrowing power" actually measures

Borrowing power, sometimes called serviceability, is a lender's estimate of the maximum loan amount you could service based on your income, expenses, and existing debts. It's not a fixed personal attribute — it's the output of a specific lender's calculation, run against that lender's own policy settings, at a specific point in time. Change the lender, and the same financial position can produce a different number.

For investors, serviceability assessment has some added layers compared with an owner-occupier loan, because a lender has to account for rental income, the fact you may hold multiple properties, and the general risk profile of investment lending. Understanding the mechanics helps explain why your borrowing power might look different from a rough online estimate, and why it changes as your portfolio grows.

02The main inputs lenders assess

Income. Lenders typically start with your gross income from employment or business, then apply their own policies to other income types. Bonus, overtime, and commission income are often only partially counted, or require a track record over a minimum period before being included at all.

Rental income, with a haircut applied. This is a key difference for investors. Lenders generally don't count 100% of a property's rental income toward serviceability. Instead, they apply a shading factor, commonly discounting the rental income by some percentage to build in a buffer for vacancy, maintenance, and management costs. The exact shading percentage is set by each lender's own policy and can vary depending on the loan and property type, so it isn't something to assume a fixed figure for.

Existing debts, assessed at a buffer rate, not the actual rate. This is the second major factor specific to serviceability. When a lender assesses your existing home loan, investment loans, car loans, or credit card limits, it typically doesn't use the interest rate you're actually paying. Instead, it applies an assessment rate that includes a buffer above the current rate, and for credit cards, it typically assesses based on the card's credit limit rather than your actual outstanding balance. This means your assessed repayment obligations are usually higher than your real, current repayments, which is a deliberate conservatism built into the process, but it also means serviceability calculations don't necessarily reflect your actual month-to-month cash flow.

The proposed new loan, also assessed with a buffer. The loan you're applying for is assessed the same way, at a buffer rate above whatever rate is actually on offer, so the lender is testing whether you could service the loan if rates rose from where they are today.

Living expenses. Lenders assess your declared living expenses against either your actual stated costs or a benchmark figure, taking whichever is higher, as part of responsible lending obligations. This includes ordinary costs like groceries, utilities, insurance, and general living costs, and can be a significant factor in the overall calculation.

Dependants and other financial commitments. Number of dependants, other loan guarantees, and any other financial commitments you carry also factor into the overall picture.

03Why a growing portfolio can reduce further borrowing capacity

Each additional investment property adds both an asset and a liability to your serviceability position. The liability side (the assessed repayment on the new loan, calculated at a buffer rate) is added in full to your existing assessed commitments. The asset side (the rental income the new property generates) is only partially counted, after shading.

Because assessed repayments are calculated conservatively and rental income is only partially offset, each additional property tends to use up more of your assessed serviceability capacity than it replenishes, even where the property is genuinely cash-flow positive in reality. This is one of the more common reasons investors find their borrowing power narrows as their portfolio grows, independent of whether their actual financial position has weakened. It's a mechanical feature of how serviceability is calculated, not necessarily a reflection of the quality of the investments themselves.

04Why every lender's figure is different

Because shading percentages, buffer rates, living expense benchmarks, and treatment of different income types are each set by individual lender policy, and because these policies change periodically, there is no single formula that produces "the" borrowing power figure for a given financial position. Two lenders assessing the same borrower with the same income and the same debts can arrive at materially different maximum loan amounts.

This is also why shopping a loan application around, or working with a mortgage broker who has visibility across multiple lenders' serviceability calculators, can matter for investors specifically. A borrower who appears to have limited capacity with one lender's policy settings may have considerably more room with another lender whose shading and buffer settings are more favourable to their particular income mix.

05Getting a real number

A general borrowing power calculator, including the affordability calculator on this site, is useful for a rough, directional estimate based on common assumptions, but it can't replicate any specific lender's actual policy. For an accurate, current figure that reflects a specific lender's rules, a mortgage broker is generally the most direct path, since brokers have access to serviceability calculators across a panel of lenders and can identify which lenders' policies suit your specific income and debt structure.

Borrowing capacity is also closely tied to the loan-to-value ratio a lender will approve and the security you're offering — see LVR and lending for investors in Australia for how those pieces fit together.

This article is general educational content, not personal financial or lending advice. Every lender's serviceability policy, buffer rate, and income-shading approach differs and changes over time. Speak with a mortgage broker or lender directly for a borrowing power figure specific to your circumstances.